Electrically heated windows have been used in vehicles to defrost or defog a transparent element comprising the window. An electrical resistance element, preferably in the form of a thin transparent metal or metal oxide electroconductive film on a transparent surface is connected to a source of electric power through a pair of bus bars. The prior art also developed a detector circuit for certain of these heated windows to alert vehicle occupants of a defective condition that may make the heating circuit inoperative, e.g. a crack or other discontinuity in the heating circuit's bus bars.
Prior to this invention, each bus bar was connected individually to a lead line unique for said bus bar, regardless of whether the bus bar was part of a transparent heating circuit for the window or incorporated in a detector circuit. Each bus bar was connected within the outline of the window to the inner end of a first terminal that extended outside the window for individual connection to an external terminal which is connected to a generator or alternator or some other electromotive source. The first terminal was laminated into the window prior to shipment to an assembly plant where each first terminal was separately attached to an external terminal corresponding to each first terminal in a time consuming operation. Some of the developments in this art prior to this invention are recited in a description of various patents that follows.
U.S. Pat. No. 4,100,398 to Levin provides a connective tab 50 of electroconductive metal embedded in an edge portion of a window. An external terminal portion of tab 50 extends outside the edge of the window for connection to a single wire harness when the window is assembled at a vehicle assembly plant. The terminal connections are encased within a sleeve of heat-shrinkable material. While the assembly at a vehicle assembly plant is accomplished in less time than an assembly that involves soldering, this patent requires that a separate connection step be performed for each bus bar.
U.S. Pat. No. 4,278,875 to Bain shows heated aircraft windows in which bus bars 24 and 26 of one embodiment and 48 and 50 of another embodiment extend from opposite sides of one end of the respective windows. Inherently, each bus bar must be secured to an external electroconductive terminal in a separate operation. In U.S. Pat. No. 4,320,286 to Barrup and U.S. Pat. No. 4,323,726 to Criss et al., the ends of bus bars also extend from the outline of windows by a spacing approximating the width dimension of the windshield, which inherently requires a separate connecting step for each bus bar.
U.S. Pat. No. 4,786,784 Nikodem, et al. shows a heated windshield with a pair of electrical leads that can be attached to connector sections 21 and 23, respectively, for connection to a vehicle's electrical system using separate connecting steps for each connector section. This patent suggests that a portion of glass sheet 14 and intermediate sheet 13 must be cut out in order to provide good solder joint strength between leads 25 and 26 and connector sections 21 and 23.
U.S. Pat. No. 4,808,799 to Schave and U.S. Pat. No. 4,829,163 to Rausch et al. show separate connections for bus bars 28 and 32 of a heating circuit and to sense line 36 of a crack detector circuit, and separate connections 24 and 26 to bus bars 20 and 22 and a sensor terminal 36 for a sensor conductor 34, respectively. Each of these patents needs to make at least three separate exterior connections.
U.S. Pat. No. 4,820,902 to Gillery discloses a dual feed bus bar arrangement for a heated transparency. A jumper wire makes it possible to reduce to two the number of leads extending from the windshield to the power source, but it extends outside the windshield enroute from one lower end to the other lower end of the extensions for the upper bus bar thus exposing the heated windshield to possible breakage of the jumper wire during certain handling steps involved in the fabrication of the windshield, particularly when it includes a roller prepress step. There is no teaching of constructing and arranging the bus bars and their terminal connections to connect them to corresponding terminal connectors for the poles of the electric power source other than separately.
A copending application, U.S. Ser. No. 07/591,917 to Bartrug et al., filed Oct. 2, 1990 reduces the likelihood of breaking the jumper wire by having the jumper wire extend between the ends of the extensions of the upper bus entirely within the margin of the windshield and laminating the entire length of the jumper wire between the windshield's glass sheets. The teachings in this copending application is incorporated by reference in this specification.